The atom is a structure in which matter is organized in the physical world or in nature. Atoms form the molecules, while atoms in turn are formed by subatomic constituents such as protons (positively charged), neutrons (uncharged) and electrons. (with negative charge).
For example, let's imagine we have a piece of iron. We split it. We still have two pieces of iron but smaller. We will leave them again, again ... Each time we will have more smaller pieces until there will come a time, that if we returned it from what we would have left it would no longer be iron, it would be another element of the periodic table. At this time, we can say that what we have left is an atom, an iron atom.
In a more formal way, we define the atom as the smallest particle into which an element can be divided without losing its chemical properties.
The origin of the word atom comes from the Greek, which means indivisible. At the time these particles were baptized, it was believed that they could not be divided, although today we know that atoms are made up of even smaller particles, distributed in the two parts of the atom, the so-called subatomic particles.
What are the parts of an atom?
The atom is divided into two parts: the nucleus and the cortex. The nucleus, in turn, is made up of neutrons (with neutral charge) and protons (with positive charge). The crust, however, is formed solely by electrons (with negative charge).
The negatively charged electrons are the lightest subatomic particles. The positively charged protons weigh about 1,836 times more than electrons. Neutrons, the only ones that have no electric charge, weigh approximately the same as protons.
Protons and neutrons are grouped in the central part of the atom formed by the atomic nucleus. For this reason they are also called nucleons. The energy that holds neutrons and neutrons together is nuclear energy;
Thus, the central part of the atom, the atomic nucleus, has a positive charge in which almost all of its mass is concentrated, while in the foreshortening around the atomic nucleus there is a certain number of electrons, negatively charged. The total charge of the atomic nucleus (positive) is equal to the negative charge of the electrons, so that the total electric charge of the atom is neutral.
This description of the electrons orbiting the atomic nucleus corresponds to the simple Bohr model. According to quantum mechanics, each particle has a wave function that occupies all the space and the electrons are not located in orbits although the probability of presence is higher at a certain distance from the nucleus.
What are the nuclear properties of the atom?
The basic units of chemistry are atoms. During chemical reactions atoms are conserved as such, they are not created or destroyed, but they are organized differently creating different bonds between one atom and another.
Depending on the composition of each atom, the different chemical elements represented in the periodic table of the chemical elements are differentiated. In this table we can find the atomic number and the mass number of each element:
- Atomic number, represented by the letter Z, indicates the amount of protons that an atom has, which is equal to that of electrons. All atoms with the same number of protons belong to the same element and have the same chemical properties. For example, all atoms with a proton will be hydrogen (Z = 1), all atoms with two protons will be helium (Z = 2).
- Mass number, is represented by the letter A, and refers to the sum of protons and neutrons that the element contains. Isotopes are two atoms with the same number of protons, but different numbers of neutrons. Isotopes of the same element have chemical and physical properties that are very similar to each other.
What does it mean that an atom has isotopes?
It happens that the atoms of an element do not all have the same number of neutrons in the nucleus. This is called isotope. Isotopes have (almost) the same chemical properties, but other physical properties. More than one isotope of virtually all elements is known. In addition, it is possible to produce new atoms with nuclear reactions, but they are often unstable and suffer from radioactive deterioration.
Isotopes are very important in the nuclear energy industry since manipulating them can generate more unstable variants ( isotopes) that favor nuclear fission reactions. Uranium enrichment is about converting a uraniumisotope into another more unstable uranium isotope.
History of atomic theory
The concept of atom is very old. Even Demokritos suggested that everything is made of atoms and emptiness, and because there is no emptiness in atoms, they are indivisible, because only emptiness can separate the songs from each other.
The concept of atom in chemistry was introduced by John Dalton in the early 19th century. With this, he explained in particular the law of multiple weight coefficients. This law says that if two elements form more than one compound, then the quantities of an element that can match the same quantity of another element are in a simple, generally small, whole proportion.
At the beginning of the 19th century, this theory and chemical reactions allowed us to determine very closely the relationship between the masses of atoms of different elements. However, it was not yet known how large their masses were in a fraction of a gram, only their relative masses were known. Therefore, it was necessary to introduce a special unit of atomic mass that was initially defined as the mass of the hydrogen atom. (Today it is defined as 1/12 of the mass of carbon-12 atom).
At the same time, thermo-theory and the closely related kinetic gas theory, which also required gas consisting of molecules, also developed rapidly. Avogadro's Law, based on the theory of kinetic gas. It was also useful for determining the atomic masses of gaseous elements.
However, in the 19th century, atomic theory was of particular importance in organic chemistry. Through various chemical reactions, powerful conclusions were drawn about the structure of organic molecules and the order in which the atoms are located together. When much later the structures of the organic molecules could also be studied with X-rays, the conclusions made by the chemists proved to be correct in most cases.
Atomic theory was quickly accepted by scientists, although there were still doubts in the late nineteenth century, for example Ernst Mach. Only the results of the radioactivity and the explanation of Albert's movement by Albert Einstein in 1905 finally resolved the dispute and allowed to determine the relationship between the unit of atomic mass and the gram.
Dalton and the scientific community long after him maintained the indivisible atom. However, the study of electrolysis towards the conclusion that the atom can obtain an electric charge, that is, ionized, gradually led to the assumption that there are also smaller electrically charged particles.
A little over 2,000 years ago, the philosopher Plato introduced atoms into various elements of the timios. He combined a regular polygon, the so-called platonic piece, in each classical element: earth, air, fire and water, so that the earth was equivalent to a cube, an air octahedron, a water icosahedron and a fire tetrahedron. Plato thought that each element was formed by its own atoms, as current theories assume.
Of the current atomic models, based on scientific findings, the first is the bulb pattern of the electron scavenger Joseph Thomson. It had been found that the atom was electrically neutral but was made up of charged particles of different brands. According to classical theory, the only possible permanent atomic model was one in which the positive and negative particles are distributed uniformly to the atom.
However, Ernest Rutherford did an experiment in which he bombarded a thin gold foil with alpha particles. To his great surprise, he discovered that a small part of the particles bounced through the others, as if the majority of the atom was empty and only a small nucleus contained the entire mass. Rutherford ended up in a solar system model where electrons circulate a positive nucleus in the same way as the planets of the sun. However, Rutherford's atomic model would not be stable, according to classical physics, because the electrons in the circular motion would soon radiate their energy.
Niels Bohr solved the problem by arguing that electrons circulate the nucleus only in certain permanent stationary paths. In the Bohr model, electrons are only emitted when they move from one track to another when absorbing or emitting a photon. The weaknesses of the model are related to the fact that in no way explains this.
Finally, physicists such as Erwin Schrödinger received the quantum mechanics developed. The atomic model in which electrons form probability clouds around the nucleus: you never know for sure where the electron is, but it is as if it extended through space. Due to the complexity and rationality of quantum mechanics, the simple models of Rutherford and Bohr are still used in teaching, and most people still think of atoms as small solar systems. However, the quantum mechanical atomic model has proven to be valid in many extreme experiments.